The present invention relates generally to light-emitting display systems and more particularly to systems having cathode-ray tubes.
Human vision is a very poorly understood mechanism that translates photons of various wavelengths into visual pictures that human brains can understand and respond to. The human vision system compensates for scenes under various illumination sources and provides to the viewer a xe2x80x9ccorrectedxe2x80x9d visual picture. For example, white tee shirts appear white in human vision regardless of whether the scene happened under sunlight, incandescent light, fluorescent light, or combinations of the aforegoing. When light emitting color display systems are exposed to similar illumination environments, the resulting images appear visually profoundly different.
Although there has been little research into producing realistic colors under different lighting conditions for light emitting color display systems beyond reducing glare, extensive research has been undertaken to predict a mathematical construct for an image called the White Point (WI). The WP is the illumination that occurred at the brightest point in the image and represents what should be considered xe2x80x9cwhitexe2x80x9d in the final image. It is assumed that every image has some white objects or highlights in it. When the brightest object, with roughly equal amounts of red, green, and blue is found, the WP operation is constructed by determining the multipliers of the red, green, and blue parts of the brightest point so that the resulting red, green, and blue values will be made equal. Once this transformation is known for the brightest point in an image, it is simultaneously applied to all the other points (which are called dots) in the image. The WP operation typically results in a final image that looks much more realistic with respect to its color balance.
There is a significant shortcoming of the simplistic WP operation described above. It is the assumption that there are some spectrally xe2x80x9cwhitexe2x80x9d objects in the image. While this is true the majority of the time for typical pictures, there are also numerous cases where a spectrally xe2x80x9cwhitexe2x80x9d object is not present. For example, a close-up picture of a red barn with some blue and green metal signs attached to the barn""s side. The dominant color would be red. If the large amount of red is diagnosed as a color cast problem, the brightest part of the image would be the green signs. If the green area is used as the WP, then the resulting picture would be made very blue.
A great deal of research is being conducted in the area of photography to see if the WP of an image can be deduced from just the image itself. However, examples like the barn picture described above will always cause problems.
An alternative solution is to measure the image""s illumination source directly. In black and white photography, the measurement was performed with a xe2x80x9clight meterxe2x80x9d. The meter is pointed at the light source, which would be straight up for daylight or towards a spotlight if it were focused on the object of interest. In color photography, a more sophisticated type of xe2x80x9clight meterxe2x80x9d called a photo spectroradiometer is used. Rather than measuring a single quantity like the black and white light meter, a photo spectroradiometer has to measure numerous points across the visual light spectrum and make a graph of the power at each wavelength that it has found. Once this graph is known, then an accurate representation of the original image can be constructed by removing the influence of the light source from the original scene. For example, an image of a white tee shirt at sunset will have a definite red cast to it. The photo spectroradiometer graph will show strong photon power in the red region of the visible spectrum. Knowing how much influence the illumination source had on the resulting image, a mathematical process is performed to remove the dominant red from the image. The final image has the white tee shirt looking truly white. In the other example of the red barn with the blue and green signs, the photo spectroradiometer graph would show normal daylight present as the illuminant. This means that almost no color correction would be applied to the final image. So in this case the dominant red barn color would be left in the image since that is the normal color that human vision would have seen under midday circumstances. The photo spectroradiometer is the ideal instrument for taking color pictures.
The problem is that a spectroradiometer is both big and expensive. A typical unit is 10 by 6 by 4 inches in size and costs between $5000 to $50,000 in 1998 dollars. It also requires a computer to readout its graphical data and apply it to the image in question. Such a system would be totally inappropriate for determining the WP for a light emitting display system for a $500 to $5000 computer or monitor.
Another problem related to light emitting display systems is that age affects the light emitted by a display system, especially the phosphors for a cathode ray tube. Thus, a system for maintaining consistent light from the display systems has been problematic.
The present invention provides a light-emitting color display system having an optical sensor system in which a plurality of photosensors are directed towards the light source of a light-emitting color display system to provide outputs proportional to the light energy associated with each color. A processing system responds to the outputs over time with the initial outputs and provides a mechanism to correct color changes in the display system.
The present invention further provides a color light-emitting display system having a second plurality of photosensors directed away from said light-emitting color display system for providing outputs proportional to ambient light and allowing adjustment of the light-emitting color display system due to changes in the ambient light.
The present invention further provides the second plurality of photosensors capable of determining the presence of illumination from natural, artificial, and combination sources to maintain the white point of the light-emitting color display system.
The present invention provides a cathode-ray tube having an optical sensor system in which a plurality of photosensors are directed towards the light source of a cathode-ray tube to provide outputs proportional to the light energy associated with each color. A processing system responds to the outputs over time with the initial outputs and provides a mechanism to correct color changes in the display system.
The present invention further provides a cathode-ray tube having a second plurality of photosensors directed away from said cathode-ray tube for providing outputs proportional to ambient light and allowing adjustment of the cathode-ray tube due to changes in the ambient light.
The present invention further provides the second plurality of photosensors capable of determining the presence of illumination from natural, artificial, and combination sources to maintain the white point of the cathode-ray tube.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.